Study On Catalytic Synthesis Of Cyclohexylbenzene From Benzene And Cyclohexene By Modified Molecular Sieves

Cyclohexylbenzene is an important chemical product with high added value.Due to the high boiling point and freezing point close to room temperature,it has special physical and chemical properties.One of the main applications of cyclohexylbenzene is an additive for lithium-ion batteries,which has anti overcharge properties and can improve the safety performance of lithium-ion batteries.In addition,cyclohexylbenzene is also a raw material for the synthesis of liquid crystal materials for thin film transistors,and it can be also used as a blending component to be added to diesel fuel.In addition to the above applications,the peroxidation reaction of cyclohexylbenzene can prepare phenol and cyclohexanone in the case of excess acetone at present,which can effectively solve the problem of excess acetone in the preparation of phenol by the isopropylbenzene process.In this paper,the modification of molecular sieves were investigated by using three different techniques and their properties such as the morphology,structure and acidic were characterized and analyzed.Furthermore,they were applied them to the alkylation reaction of benzene with cyclohexene for synthesizing cyclohexylbenzene.The reaction mechanism of alkylation was proposed according to the experimental results from gas chromatography-mass spectrometry analysis,and the suitable production processes of cyclohexylbenzene were given by process optimization,catalyst lifetime and activity stability study.（1）Solid acid catalysts of molecular sievesβloaded with anhydrous Al Cl₃ were prepared by the impregnation method,and their morphology,structure,and specific surface area,etc were characterized for their morphology and structure.It was shown that the strong acid amount of the catalyst was enhanced by the loading of aluminum trichloride on theβ-molecular sieve,and the conversion of cyclohexene was improved.The main factors influencing the alkylation of benzene and cyclohexene were also investigated,and the optimum reaction process conditions were determined by single-factor-multi-level experimental method.Under the optimal process conditions of 10%Al Cl₃/H-βloading as catalyst,15 molar ratio of benzene to cyclohexene,100%of the mass of cyclohexene as catalyst,80℃and 3 h,the conversion of cyclohexene was over 99%and the selectivity of cyclohexylbenzene was 60.28%.（2）The molecular sieve USY were modified with ammonium nitrate,hydrochloric acid,urea and sodium hydroxide solution by liquid phase ion exchange method,and molecular sieve catalysts with different properties of acidity and pore structure H-USY were prepared.The results showed that the modified molecular sieve could greatly improve the alkylation reaction of benzene with cyclohexene due to the increase of BET specific surface area,BJH pore volume pore size and acidity of H-USY.The results of process optimization experiments showed that the alkylation of benzene with cyclohexene was carried out by using the molecular sieve catalyst H-USY（2）obtained by secondary modification with ammonium nitrate exchange,According to the following conditions:the molar ratio of benzene to alkene was 15,the reaction temperature was 80℃,the reaction was 4 h,and the catalyst dosage was 4%of the total mass of the reactants,the conversion of cyclohexene reached 95.34%,and the selectivity of the product cyclohexylbenzene was 97.44%.We also found the same effect with urea-modified USY and above alkylation reaction showed a conversion of cyclohexene of 96.14%and a selectivity of cyclohexylbenzene of 94.92%.（3）H-La-Y and La-H-Y molecular sieves catalysts with different La³⁺loadings were prepared by the impregnation-ion exchange method.These catalysts were characterized and analyzed,and the alkylation performance of the modified molecular sieves for catalyzing the synthesis of cyclohexylbenzene from benzene and cyclohexene was investigated.The experimental results showed that the introduction of the backbone of La³⁺and the exchange of cations led to more strong acid centers in the H-Y molecular sieves,which greatly improved the acid strength of the molecular sieves and the conversion rate of cyclohexene.It was found that the La-H-Y（2）molecular sieve had a high activity.Under optimum conditions,the alkylation of benzene with cyclohexene using La-H-Y（2）molecular sieve as catalyst resulted in a conversion of 98.27%of cyclohexene and a selectivity of 97.63%of the product cyclohexylbenzene.In addition,the TG-DSC analysis before and after the reaction showed that a small amount of organic matter was retained in the pore channels after the reaction,and the regeneration of the catalyst by roasting after use would lead to the destruction of part of the molecular sieve skeleton structure,and its regeneration needs to be further investigated.